Air source heat pump cost by property size
Prices below are for supply and full installation including the outdoor unit, indoor cylinder, controls, and commissioning. They exclude radiator upgrades or new pipework, which can add £1,000-£4,000.
| Property size | Typical output needed | Supply & install cost | After £7,500 grant |
|---|---|---|---|
| Small flat / 1-2 bed | 4-6 kW | £8,000 - £11,000 | £500 - £3,500 |
| 2-3 bed semi-detached | 6-8 kW | £10,000 - £13,000 | £2,500 - £5,500 |
| 3-4 bed detached | 8-11 kW | £12,000 - £16,000 | £4,500 - £8,500 |
| 4-5 bed large detached | 11-14 kW | £14,000 - £18,000 | £6,500 - £10,500 |
Costs are indicative UK averages for 2026. London and South East installations typically run 15-20% higher.
What affects the cost of an air source heat pump?
Several factors push prices up or down significantly:
- Property size and heat loss: larger, poorly insulated homes need a bigger (more expensive) unit and may require insulation work first.
- Radiator compatibility: ASHPs work best at lower flow temperatures, so older, undersized radiators may need upgrading to larger panels or underfloor heating — budget £1,000-£4,000.
- Hot water cylinder: most gas boiler homes will need a new unvented hot water cylinder (£800-£1,500 if not already present).
- Existing system type: replacing a combi boiler is more involved than converting a system with a cylinder already.
- Brand and model: premium brands (Mitsubishi, Vaillant, Daikin) cost more but often carry longer warranties.
- Groundwork and location: external unit positioning, concrete pad, and pipework runs all affect labour time.
- Region: London and the South East are typically 15-20% more expensive than the national average.
- Scaffolding or access requirements for pipework routing through the building.
Running costs and efficiency
A modern air source heat pump achieves a coefficient of performance (COP) of 2.5 to 4.0, meaning it produces 2.5-4 units of heat for every unit of electricity used. At a typical 2026 electricity rate of around 24p/kWh and Ofgem-capped gas at around 6p/kWh, the economics depend heavily on your tariff.
For a well-insulated 3-bed semi with an annual heat demand of around 12,000 kWh, running costs with an ASHP at a COP of 3.0 might be approximately £960/year in electricity, compared with around £840/year in gas at 60% boiler efficiency. The gap narrows on an EV-style overnight tariff (as low as 7-12p/kWh), where an ASHP can beat gas on running costs.
Heat pump tariffs such as Octopus Cosy or E.ON Heat Pump Saver can significantly reduce electricity costs for ASHP users, and are worth comparing before installation.
Over a 15-20 year lifespan, and accounting for the grant, most properties in England and Wales see a positive financial return versus replacing with a gas boiler, particularly as carbon prices and gas costs are expected to rise.
Check your home is suitable before committing
Air source heat pumps work best in well-insulated homes. If your property has significant heat loss (poor loft insulation, uninsulated walls, draughty windows), the system will struggle to keep up in cold weather and running costs will be high. Get a heat loss survey from an MCS-certified installer before signing a contract — reputable installers will insist on this.
How to get an air source heat pump installed
Follow these steps to get the best outcome and secure the grant:
Get a heat loss survey
A proper Manual J / BS EN 12831 heat loss calculation tells the installer what size unit you need. Oversizing wastes money; undersizing leaves you cold.
Obtain 3 quotes from MCS-certified installers
Only MCS-certified installers can submit a Boiler Upgrade Scheme voucher on your behalf. Compare quotes on scope, brand, warranty, and COP at your design temperature.
Check your EPC
To be eligible for the Boiler Upgrade Scheme your EPC must not have outstanding recommendations for loft or cavity wall insulation (or those measures must not be applicable). Sort these first if needed.
Installer applies for the grant voucher
Your chosen installer applies for the £7,500 voucher through Ofgem before installation starts. The discount comes off your invoice — you never handle the money.
Installation and commissioning
A typical ASHP installation takes 2-3 days. The installer commissions the system, sets flow temperatures, and hands over controls documentation.
Register the system
Your installer registers the installation with MCS and, if in Scotland, with Building Standards. Keep all paperwork for future property sales and warranty claims.
Plan your budget before you buy
If you are buying a property with an old gas boiler and are considering switching to a heat pump, our home-buying planner helps you build a realistic refurbishment reserve into your offer and affordability calculations — so you know the true cost of ownership from day one.